Early transition metal catalysts for olefin polymers by coordination polymerization are well-known, typically those are the traditional Ziegler-type catalysts based on Group 4 and 5 of the Periodic Table (IUPAC new nomenclature) and the newer metallocene catalysts based on Group 4–6 metals. However specific late transition metal catalysts suitable for olefin polymerization had not offered the same levels of activity or molecular weight capability for olefin polymerization during the development of these catalyst systems and additional work was published addressing this lack.
In Johnson, Killian, and Brookhart, J. Am. Chem. Soc., 1995, 117, 6414 the authors describe the use of Ni and Pd complexes for the solution homopolymerization of ethylene, propylene, and 1-hexene. The catalyst precursors are square-planar, M2+, d8, 16 electron complexes incorporating substituted, bidentate diimine ligands. The active coordination sites are occupied by either methyl or bromide ligands. Methyl ligand complexes were activated with H+(OEt2)2[B(3,5-(CF3)2C6H3)4]− and bromide ligand complexes were activated with methylalumoxane (MAO) or diethylaluminumchloride as cocatalysts.
European patent publication EP-A2-0 454 231 describes Group VIIIb metal catalysts said to be suitable for the polymerization of ethylene, α-olefins, diolefins, functionalized olefins, and alkynes. The described catalyst precursors are Group VIIIb metal (Groups 8, 9, 10, IUPAC new nomenclature) compounds which are subsequently activated by compounds including discrete borate anions. Ethylene homopolymerization in solutions of methylene chloride, toluene and diethyl ether are illustrated. Few polymerizations were conducted in the presence of a support material and broad molecular weight distribution polymers were produced.
The advantages recognized with the early transition metal catalysts of immobilizing the catalyst on solid supports to enable heterogeneous polymerization processes such as those based on gas phase, bulk or slurry processes would be important to effect efficient industrial utilization of the late transition metal catalysts described, and derivatives of them. In particular, due to the observed high levels of branching with the catalysts of the above literature, melting points of the resulting polymers were anticipated to be so low as to present problems with reactor operation at typical industrial operating temperatures occurring when heat dissipation by solvents is unavailable, as in continuous gas phase polymerization.